Conventional gas turbine engines having centrifugal compressors typically have an axial cold clearance between the impeller and the impeller shroud set such that a rub between them will not occur at the operating conditions that will cause the highest clearance closure which is typically a cold burst. Active clearance control systems have been developed to control radial turbine clearances between tips of axial flow radially extending turbine and compressor blades and shrouds surrounding the blades. Typically, these active clearance control systems are thermally activated and use relatively cold or hot air or a combination of both from the fan, different compressor stages, or compressor discharge air to thermally cool or heat turbine or compressor shrouds or shroud support structures or casings in order to reduce the operating radial clearances. Controlling radial turbine clearances between tips of axial flow radially extending turbine and compressor blades and shrouds surrounding the blades increases fuel efficiency and reduces wear on the blades due to rubs.
It is known in the art to minimize clearance between the blade tips of an impeller rotating within a gas turbine engine and a surrounding blade tip shroud to reduce leakage of a working fluid around the blade tips of centrifugal compressor stages. Several actuation systems for adjusting blade tip clearance during engine operation have been developed. These systems often include complicated linkages, contribute significant weight, and/or require a significant amount of power to operate. Thus, there continues to be a demand for advancements in blade clearance technology to decrease impeller tip clearance thus causing an increase in overall compressor efficiency.